Activity Sampling.ppt 1

8/3/2019 Activity Sampling.ppt 1

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Activity Sampling

IntroductionConstruction work involves the employment of different kind of

people for different situations.

To record the level of productivity in these conditions is not easily

achieved, because conditions are rarely are conditions stableenough for clear process to take place.

The reason is, in construction industry output of a worker may vary

over a wide margin, because of

bad weather condition,

machine breakdowns,

poor communication, etc.

The time between observation and report is usually too long to

pick up in efficient sections of work quickly enough for corrective

action to be taken.


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Activity Sampling

Introduction

The technique call activity sampling is a

method which provides the project

manager with a fairly sensitive

management tool to do a similar job to

time study methods without many of its

disadvantages when applied toconstruction work.


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Activity Sampling

Introduction - Example First occasion Eight men taking near excavation (road

side)

Second occasion The place was deserted

Third occasion Four men watching, one man priming

a pump, one man holding a pneumatic hammer

Fourth occasion Four men near excavation

Fifth occasion

Six men watching, one man working

Sixth occasion Seven men watching one man at work

Final disappointment for some time but excavation

was finally filled done


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Activity Sampling

Field Count

Obviously if the rating causes concern,

further investigation may be warranted


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Activity Sampling

Field Count

Obviously if the rating causes concern,

further investigation may be warranted


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Activity Sampling

Field Count The total number of men observed should be between

7580% of the total employed workforce.

Clearly the field count technique can only provide a

guide since the number of observa-tions is so few.

The following example illustrates the use of statistics in

turning the method into something more meaningful.


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Activity Sampling

Field Count Example

A field count indicates that about 40% of the available

work time on a section of construction work is spent on

unproductive work. How many observations arerequired to be sure that the proportion is within 2%

accuracy? Given that 95% confidence is required.

If the field count is repeated on many occasions and the

proportion of unproductive workers plotted graphically,it is quite likely that the data will fit a normal distribution

as illustrated in Fig. 2.3. Such data can then be

interpreted statistically in the following way.


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Activity Sampling

Field Count Example


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Activity Sampling

Field Count Example

By substituting for in equations (1) and (2)

0.02 = 2 x [P (1-P)/n]

n = 4 x 0.4 (1 0.4)

0.022

n = 2400 observations

Therefore by taking 2400 observations the proportion of

underproductive work is determined to within 2%

accuracy.


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Activity Sampling

Activity Sampling Procedure1. First, carry out a preliminary survey to get a feeling for

the problem. The information collected will help in

deciding on the size of the section of work to be studied

and the number of workers involved.2. Identify the workers by name, and list the operations

and tasks to be studied. Sometimes this need only be

Working or Not working, but for a much fuller

investigation greater detail will be required, such asFixing formwork, Cleaning shutter panels, Receiving

instructions etc.

3. Prepare a suitable observation sheet (Fig. 2.4) for

recording the information.


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Activity Sampling

Activity Sampling Procedure4. Consult the supervisor of the work and ensure that

everyone is fully informed. Failure to do so may cause

unrest, which can quickly escalate and feed smoldering

grievances.5. The number of observations required is normally quite

large; therefore, a planned timetable of observation

times should now be assembled. In mass production

work these times are normally chosen ran-domly sincethe work patterns tend to be regular. However, in

construc-tion work, activities by their very nature take a

random time to complete and thus the observations can

be taken at regular intervals. Even so, caution is

required with some types of building work, e.g.


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Activity Sampling

Activity Sampling Procedure6. Choose a suitable position for taking the observations.

7. Record each activity that is in operation at the instant it

is observed, together with the worker involved.

8. From the percentages of the activities observed select

the activity or activities which show a disproportionate

amount of time being spent on them. Corrective action

can then be considered.


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Activity Sampling

Activity Sampling Procedure


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Activity Sampling

Output Rates The Activity Sampling technique can, if carefully

applied, is used to determine production output data for

use in estimating and planning the duration of activities.

When recording the number of observations for eachoperation, the performance level of the operative, or

machine etc. is assessed at each observation on the

standard rating scale described in the previous chapter

under TimeS

tudy and the mean rating for the operationtogether with time spent as a proportion of the whole

activity are calculated. If the total elapsed time of the

activity is also recorded, then the basic times of the

individual operations in the task can be calculated.


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Activity Sampling - Assignment

Perform a activity sampling for siteoperation such as brickwork,

formwork fixing or reinforcement.

Write a short report based on yourobservations.

Activity Sampling.ppt 1

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